View Full Version : Other products similar to Babolat RDC/Prince Precision Tuning Center?

03-13-2012, 05:33 AM
I am looking to get a machine that will calculate swingweight and static weight. I am also not looking to spend $2,000-5,000. Are there any more economic options that will do the same thing or anything somewhat cheaper from other companies?

03-13-2012, 06:53 AM
Well there is an app called RacquetTune developed by Sten Kaiser used for tuning your racket. Just as a disclaimer Sten by the way does not agree with me on this one by the way but I think I am right.

I have an idea for a way to support a racket by the handle that allows the racket to swing freely. The RacquetTune app can also be used to time the pendulum swings of bats and other sport tools so why not a tennis racket.

Rod Cross and Crawford Lindsey said, in The Physics and Technology of Tennis (http://www.tennis-warehouse.com/descpage-PHYSICS.html), "Ideally, one should swing the racquet about the actual axis of ratation of interest (near the end of the handle), but it is not easy to mount a racquet in that way." Well here comes another disclaimer I think I can do it very easily.

If you look at all the machines like the Babolat, Prince and Gamma machines they all measure the racket at a point 10 cm from the butt cap. That distance is used because that is the average pivot point for tennis players. Most tennis players don't grip the racket at that point most are either higher or lower than 10 cm. Anyway the racket is pushed out a set distance and the time it takes the racket to rotate against a known force is measure to come up with the center of mass (COM) relative to the pivot point (PP.) The distance from the COM - PP is very important when computing swing weight (SW) because SW is the relative mass at the COM relative to the PP time the distance from COM to PP squared.

One very important point I would like to make is the COM I am speaking of is not the balance point of the racket. It is relative to a pivot point. The only way I think you can identify that point is the set the racket in motion at the pivot point and measure the pendulum cycle and calculate the distance based on the time it takes to cycle.

Let's assume now you have a racket support at PP and the distance to the COM is 35.0 cm. With the racket support at the PP the COM weight measures 250 g. My swing weight will be .25 kg x 35 cm x 35 cm or 306.25 kgcmcm.

Now let's assume you take the same racket but you don't know where the COM is you measure the weight at a point 40 cm from the PP and you get 219 g. Because the COM is the center of gravity of the racket the effect it has at all points will be the same so the product of the m x d will be about 8.75 kgcm of force. As the distance gets longer the weight (leverage or force goes down) and the distance gets shorter the weight goes up. All this gives you nothing more than the first moment or the moment of inertia (MOI) relative to the PP. If you can get the COM relative to the PP and multiply the MOI by that distance you have the swing weight.

I know all this may seem confusing and for right now it is nothing more than an idea in my head. I need to test it out but I think I am right. When I get some time I plan to test it and make a video.

Here is the short version. Make your pivot 'thing-a-ma-jig' out of an ice cream stick cut it half and two nails. Glue the nails on the two stick so it is perpendicular to the stick. Hold the racket in your hand ad the point where the center your index finger knuckle hits the is your PP. Put the stick on the racket so the nails stick out in opposing side of the handle and hold them on with a rubber band. The nails should be centered on your PP. The less the jig weighs the less error in your SW. Let the racket swing and use the RacquetTune app to get your time. Find the formula to calculate the distance in cm Support the racket at your PP and weight the racket at some point above the PP I would use 40 cm. for a general rule the COM will move up from the balance point of the racket by the distance from the butt cap to your PP but that is not exact.

SW = weight in kg x distance measuring point x calculated distance of cycle.

If there are any engineering or physics X-Sperts out there that can shoot some holes in my theory I would love to hear from you. I know this is rough and confusing but I can go on if needed.

03-14-2012, 02:42 AM

03-14-2012, 04:30 AM
I thought the Accuswing (http://tt.tennis-warehouse.com/showthread.php?t=103330) was discontinued. I will check with Alpha tennis later and find out.

03-14-2012, 09:34 AM
Just talked to Greg at Alpha sports and he said the Accuswing has been discontinued for about 2 - 3 years. In the spring Alpha is coming out with an Accuswing II that will sell for either $749 or $799.

EDIT: Also the Accuswing II will not have a scale and only does SW measurements.